What is the 2G / 3G network shutdown?

Mobile operators around the world are gradually decommissioning their 2G (GSM) and 3G (UMTS) networks. This allows them to reuse spectrum and network resources for other technologies such as LTE-M, NB-IoT, LTE and 5G. Shutdown dates vary by country and operator. Once the last network supported by a device is switched off in a particular location, the device will no longer be able to connect there until its connectivity or hardware has been upgraded or replaced.